RA1 focuses on the development of Earth system models and their application to learn about the character, scope and significance of feedback mechanisms linking the biosphere and atmosphere, globally and in contrasting regions and climate zones of the world.

A core ambition of MERGE is to advance the frontiers of knowledge surrounding the role played by ecosystems and the land surface – the terrestrial biosphere – in the climate system of the Earth. The biosphere affects the energy balance and radiation retention properties of the atmosphere via biogeophysical and biogeochemical feedback mechanisms, involving for example the amount of sunlight absorbed by vegetation, the evaporation of water from foliage and the soil surface, and the net uptake or release of carbon dioxide and other greenhouse gases due to ecosystem processes like photosynthesis, soil organic matter decomposition, wildfires and human land use.

Computer models are needed to adequately represent the complexity and vast scale of the climate system. Traditionally known as general circulation models (GCMs), as they incorporate representations of processes beyond the physics of the atmosphere and oceans, they are coming to be known as Earth system models (ESMs).

Models

The Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) is a globally-applicable model of vegetation dynamics and ecosystem biogeochemistry, a so-called dynamic global vegetation model (DGVM). It was first developed in the late 1990’s and has been used in over 100 published studies of climate impacts on vegetation and ecosystems, global and regional carbon balance, biodiversity, agricultural and forest management, and climate adaptation. LPJ-GUESS provides the biosphere component in the RCA-GUESS and EC-EARTH Earth system models, described below

RCA-GUESS is a regional Earth system model coupling the LPJ-GUESS dynamic vegetation model to the Rossby Centre Atmospheric model, RCA. It is being used to investigate the role of biogeophysical feedback mechanisms mediated by changes in vegetation patterns, species composition and land use on regional climate patterns and trends, for example in Europe, the Arctic and Africa.

EC-EARTH is a global Earth system model developed by a European consortium that incorporates LPJ-GUESS to account for biogeophysical feedbacks of vegetation changes on the atmosphere. In ongoing development it will also account for biogeochemical feedbacks due to ecosystem exchanges of carbon dioxide, other greenhouse gases such as methane and nitrous oxides, secondary organic aerosols and emissions from wildfires.